This invention relates to a device for the administration of drug and, more particularly, to a medical bandage for the controlled continuous metering of the flow of systemically active drug to the skin or mucosa over a period of time. "Systemically active" drugs, as that term is used in this specification and the appended claims, are agents which, when applied to the skin or mucosa, are absorbed through the body surface to which applied and are transported from their site of application by the recipient's circulatory system or lymphatic system, to cause a pharmacologic or physiologic response at a remote site in the body.
Systemically active drugs are conventionally administered either orally or by injection, with the primary objective of the mode being to achieve a given desired blood level of drug in circulation over a period of time. However, these prior art methods possess certain shortcomings resulting in the failure to obtain these goals. For example, the oral route is inadequate for several reasons even though the drug is administered at periodic intervals according to a well defined schedule. The rate of absorption of drug through the gastrointestinal tract is affected by both the contents of the tract and the time of passage of drug through the small intestine. Therefore, such variables as whether the drug is administered before or after eating and the type and quantity of food eaten (for example, high or low fat content), or whether administered before or after a bowel movement, affect the rate of absorption of the drug which takes place in the small intestine. Additionally, the time of passage of drug through the small intestine is affected by the rate of peristaltic contracting, adding further uncertainty. Also important is the rate of circulation of blood to the small intestine and the fact that many drugs administered by this route are rendered inactive by gastric acid and digestive enzymes of the gastrointestinal tract or liver where the drug can be metabolized to an inactive product by that organ. These factors make it difficult to achieve a desired time course of concentration of the drug in the blood. The almost inevitable result of oral administration of drugs through the gastrointestinal tract is that the level of drug in circulation surges to a peak level at the time the drug is administered, followed by a decline in concentration in the blood and body compartments. Thus, a plot of drug in circulation after administration of several tablets a day has the appearance of a series of peaks which may surpass the toxic threshold of the drug, and valleys which fall below the critical point needed to achieve the desired therapeutic effect.
The administration of drugs by injection can entail certain disadvantages. For example, very strict asepsis must be maintained to avoid infection of the blood, the vascular system or heart. Drug administration by poor intravenous injection technique may result in perivascular injection when it is not intended; and the typical result of injection into the blood is a sudden rise in the blood concentration followed by an uncontrolled decline. Additionally, administration of drugs by injection is inconvenient and painful. Other dosage forms for systemic administration of drug, such as rectal suppositories and sublingual lozenges, also produce non-uniform levels of the therapeutic agent in circulation. These dosage forms require great patient cooperation, have low patient acceptability, and are sparingly used throughout most of the world.
To avoid the problems discussed above, it has been suggested that systemically active drugs can be administered through the skin. Uncertainties of administration through the gastrointestinal tract and the inconvenience of administration by injection are eliminated. Since a high concentration of drug never enters the body, problems of pulse entry are overcome. Despite these advantages of administering systemically active drugs through the skin, prior art devices designed for this purpose do not provide continuous administration and delivery rate.